Abstract: This report investigates the failure mechanisms of shear-critical squat (ratio height to length of less than two) reinforced concrete walls, commonly used in many commercial buildings and nearly all safety-related nuclear structures. A database with experimental data obtained from 434 tests is assembled with the objective of improving the current state of knowledge on squat wall response. The adequateness of the peak shear strength prediction equations available in current design provisions is evaluated. Improved empirical equations are developed for peak shear strength prediction for rectangular walls and walls with boundary elements in a format suitable for inclusion in standards and codes of practice. Squat walls are modeled using finite elements to predict their monotonic and cyclic responses. Modeling decisions that are critical to predict the wall responses are explored and recommendations for finite element modeling are made. Macro-level hysteretic models are prepared for a small number of squat walls for which digital load-displacement data are available. The calibrated Ibarra-Krawinkler model is used to properly capture the strength, stiffness degradation, and pinching effects in the walls response. Information in the database is used to identify damage states and to develop fragility functions for buildings and safety-related nuclear structures incorporating squat reinforced concrete walls.